A cellular wireless network typically includes a number of base stations or other access nodes, referred to without limitation as Node-Bs (NBs), that are configured to provide wireless coverage areas, such as cells and cell sectors, in which user equipment devices (UEs) such as cell phones, tablet computers, machine-type-communication devices, tracking devices, embedded wireless modules, and/or other wirelessly equipped communication devices (whether or not user operated), can operate. Each NB could be coupled with a core network that provides connectivity with various application servers and/or transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the cellular network could engage in air interface communication with a NB and could thereby communicate via the NB with various application servers and other entities.
Such a network could operate in accordance with a particular air interface protocol (or radio access technology), with communications from the NBs to UEs defining a downlink or forward link and communications from the UEs to the NBs defining an uplink or reverse link.
In accordance with the air interface protocol, each coverage area could operate on one or more carriers, each of which could be frequency division duplex (FDD), defining separate frequency channels for downlink and uplink communication, or time division duplex (TDD), with a single frequency channel multiplexed over time between downlink and uplink use. Further, on the downlink and uplink, each such carrier could be structured to define various physical channels for carrying information between the base stations and UEs.
Over the years, the industry has embraced various “generations” of air interface protocols, in a continuous effort to increase available data rate and quality of service for end users. These generations have ranged from “1G,” which used simple analog frequency modulation to facilitate basic voice-call service, to “4G”—such as Long Term Evolution (LTE), which now facilitates mobile broadband service using technologies such as orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO). And most recently, the industry is now exploring developments in “5G” and particularly “5G NR” (5G New Radio), which may use a scalable OFDM air interface, advanced channel coding, massive MIMO, beamforming, and/or other features, to support higher data rates and countless applications, such as mission-critical services, enhanced mobile broadband, and massive Internet of Things (IoT).
As the industry advances from one generation of wireless air interface technology to the next, issues arise with the need for UEs to support potentially multiple air interface protocols at once. With the transition from 4G to 5G, for instance, it is expected that UEs will be configured to support use of both technologies concurrently, with an arrangement referred to as EUTRA-NR Dual Connectivity (EN-DC). With such an arrangement, a UE might include a 4G radio and a 5G radio, with the 4G radio being served by a 4G base station concurrently with the 5G radio being served by a 5G base station. This arrangement could help support transition from 4G technology to 5G technology and may provide other benefits as well. More generally, dual connectivity could encompass service on two or more air interface protocols concurrently, to facilitate technology transitions or for other purposes.